Anim: Graph Editor - automatically lock key translation to a single axis

When moving keys in the Graph Editor animators
usually only want to move them on one axis.
While this is possible in a few ways (G+X, or G + Middle Mouse Button click),
we could default the behavior to always lock on an axis.
This was suggested by Dreamworks animators during the
Animation & Rigging module meeting.
https://devtalk.blender.org/t/2024-01-26-animation-rigging-module-meeting/33081#patch-review-decision-time-5

This PR adds an option with which the movement is
always locked to a single axis by default.
The option can be found in the Graph Editor under "View->Auto-Lock Axis".

The movement will then be restricted to the axis along
which you've moved the cursor the most.
You can still manually override the lock behavior by pressing `X` or `Y`.

I am piggybacking off the auto locking feature you get when pressing the middle mouse button.
When the new feature is enabled I call that at the start of the transformation.
Except when:
* only handles are selected
* the tweak mode has been started on a handle

This is to not snap handles, which is a behavior that has
been requested by the artists.

Pull Request: https://projects.blender.org/blender/blender/pulls/117669

scripts/startup/bl_ui/space_graph.py

@@ -159,6 +159,7 @@ class GRAPH_MT_view(Menu):
         layout.prop(st, "use_realtime_update")
         layout.prop(st, "show_sliders")
         layout.prop(st, "use_auto_merge_keyframes")
+        layout.prop(st, "autolock_translation_axis")
         layout.separator()
 
         if st.mode != 'DRIVERS':